The new text sticks to previous goals, including one of limiting world temperature rises to a maximum rise of two celsius above pre-industrial times to avert impacts such as floods, heatwaves, species extinctions and rising ocean levels.

"We shall, recognising the scientific view that the increase in global temperature should be below two degrees and in the context of sustainable development, enhance our long-term co-operative action to combat climate change," the draft accord says.

'Ambitious action'

But the document leaves blank key elements such as the depth of cuts in greenhouse gas emissions expected of developed nations by 2020 and does not say which countries will be legally obliged to cut emissions by how much or when.

in depth

The accord simply states early on in the text that "ambitious action to mitigate climate change is needed with developed countries taking the lead".

Although it says that "deep cuts" in emissions are needed to reach a goal of cutting global emission by 50 per cent by 2050, specific limits of greenhouse gas emissions for the coming years were still to be set.

Earlier on Friday, world leaders had appeared to mount a last-minute bid to save the pact, but these efforts only achieved agreement on a consensus-driven deal with few specifics that many admitted would fall short of what was needed.

The tense haggling capped two years of deadlock over crafting a new UN treaty from 2013 that would reduce global warming from mortal threat to manageable peril.

But sideline negotiations have revealed deep divisions between rich and poor, entrenched in a textual battlefield over how to curb carbon emissions and muster funds to fight climate change.

On Friday, around 120 heads of states - led by a pool for around two dozen key players - struggled for at least a basic accord that would set a few targets and chart further action towards a final pact next year.

Barack Obama, the US president, admitted such an outcome was not ideal but urged the world to accept it, given the terrifying cost of disunity.

Disappointment

"I am sure many consider this an imperfect framework ... no country would get everything that it wants," he said. "The question is whether we will move forward together, or split apart."

In video

G77 negotiatior Lumumba Diaping speaks about his expectations from the final negotiations

Manmohan Singh, the Indian prime minister, acknowledged the outcome "may well fall short of our expectations" but called for follow-up negotiations to be completed by the end of 2010.

Yukio Hatoyama, the Japanese premier, who has offered nearly $20bn towards a global climate fund, said the summit would deliver a "robust" if "not necessarily perfect" statement on fighting global warming.

But Dmitry Medvedev, the Russian president, said the world community had "clearly underestimated" the task of reaching not just a binding agreement but even a general declaration.

"We still have long and difficult road ahead of us," he said.

Hugo Chavez, Venezuela's president, was bluntest: "The meeting has not been success - it has failed."

One member of the Maldives delegation, the Indian Ocean archipelago which fears being swallowed up by rising sea levels in a matter of decades, added: "Whatever the outcome, it looks bad for us."

Disunity

Delegates have blamed the US and China for slow progress on a deal, which more than 110 world leaders are expected to sign later on Friday.

Nicolas Sarkozy, the French president, said Chinese objections to a monitoring system for carbon dioxide emissions were a key stumbling block to forging an agreement.

But Wen Jiabao, the Chinese prime minister, defended his country's voluntary climate targets, telling the conference it would meet them with "real action".

Obama and Wen, and some European Union countries, continued to hold private talks late on Friday, in which further discussions on greenhouse gas emission targets, financing for climate aid and transparency in monitoring nations' pledges to cut emissions are being discussed.